WATCH: NI prepares for B-day parties and protests
Our reporters are in Newry to gauge reaction of businesses and residents
Brexit Day is expected to be greeted with both protests and some celebrations both in Northern Ireland and the Republic.
In the final hours before the UK officially leaves the EU, a series of protests have been planned along the Irish border.
Anti-Brexit campaigners will also hold a demonstration at Stormont today (Friday) afternoon, before Brexit-backers later hold a celebration party at the gates of the seat of Northern Ireland's devolved government from 10.30pm for a countdown to 11pm.
Last September, the PSNI announced that a contingency plan was in place to restrict police leave following the previously planned October 31 Brexit Day.
It came after warnings about challenges the PSNI may face following Brexit, including an uplift in dissident republican violence and potential public order situations.
Assistant Chief Constable George Clarke described it as a "sensible operational contingency'', adding that it would be kept under review.
In the Irish Republic, the UK's departure from the EU is a campaign issue in the ongoing General Election campaign.
Fine Gael Government ministers hosted a 5am tour of Dublin Port as the first ships of Brexit Day dock and unload.
Fine Gael's main rival, Fianna Fail, branded the early-morning visit a "stunt'', accusing the Government of "politicising'' Brexit.
Deputy Premier Simon Coveney rejected those claims on Friday morning.
"Whether we like it or not, Brexit is going to dominate Irish politics for at least the next 12 to 18 months,'' he said.
"I know the public are fed up talking about Brexit - so am I, quite frankly - but we don't have the luxury of not talking about Brexit and preparing for it.
"It has such an impact potentially on the future of the Irish economy and the future of the Irish fishing industry, on the future of Irish agriculture, on the future of the Irish tourism industry.
"Put quite simply, all of the plans, all of the manifestos that are being debated and discussed in this election campaign, much of that is just aspirational if we don't maintain and protect a strong economy through the challenges of Brexit.
"We felt it was important to be in Dublin Port where 60% of everything that comes into Ireland comes through, and the port, working with other agencies in the state, have spent 30 million euros to prepare for the new realities of Brexit.
"We are, as of today, Brexit-ready, and we are prepared for the new realities should there be no transition period in place.''
Later on Friday morning, Ireland's premier, Taoiseach Leo Varadkar, will give an address on Brexit in Dublin.
The Irish border, which will become the only land frontier between the UK and the EU after Brexit, dominated negotiations over three years for a withdrawal agreement, proving a sticking point amid opposition to a reinforced boundary.
Unionists have also opposed checks on the Irish Sea amid claims and counter-claims over what the reality will be for goods crossing the channel after Friday.
As 11pm draws closer, there will be protests at six points along the Irish border by the organisation Border Communities Against Brexit, from Carrickarnon just south of Newry to Aughnacloy in Co Tyrone, Aghalane and Blacklion in Co Fermanagh, the Strabane/Lifford border, and Bridgend in Co Londonderry.
The hour of the UK's departure will be marked with a celebration event at Stormont at which Union flags are expected to be waved and toasts made.
Downtown & Cool FM spent the day in Newry - one of the key border areas.
We have been gauging the views of local businesses and residents who have mixed views about leaving the EU.
Most told us they were still very unsure about what the future held.
Chloe Kimmins runs a café in Newry and she says future supplies are difficult to forecast.
She said: "A lot of our supplies are from across the border and especially our coffee it’s form Dublin and we don’t know what way the prices will range after taxes and we’ll probably have to find cheaper coffee up North.
"Coffee shops get coffees because it brings a certain crowd people that like to drink their coffee and people will travel from the south to come up here and try our coffee and that might effect it as well. People might not want to go across the border and come to Newry anymore”